Process for surface treatment of copper and its alloys



United States Patent O 3,544,389 PROCESS FOR SURFACE TREATMENT OF COPPERAND ITS ALLOYS Hargovind N. Vazirani, Stirling, N.J., assignor to BellTelephone Laboratories, Incorporated, Murray Hill and Berkeley Heights,N.J., a corporation of New York No Drawing. Filed Dec. 18, 1967, Ser.No. 691,201 Int. Cl. C23f 7/02 U.S. Cl. 148-614 9 Claims ABSTRACT OF THEDISCLOSURE This is a method for surface treatment of copper and and itsalloys which results in an improved adhesive joint between the metal andOrganic adhesive materials and comprises treatment in an alkalinepermanganate solution.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the surface treatment of copper and its alloys by use of analkaline permanganate solution, in order to improve adhesive jointsbetween such surfaces and organic adhesive materials, and also relatesto the joined product.

Description of the prior art Adhesive joining of copper and its alloysto both metals and nonmetals is common practice. Corrosion productsordinarily present on the surface of the metal interfere with suchjoining and have in the past been removed and replaced by a chemicallyproduced oxide layer which prevents further corrosion and provides asurface suitable for joining.

This layer has been achieved generally by oxidizing the surface of themetal with various solutions containing chlorite ions. See, for example,U.S. Pat. 3,198,672.

There are several disadvantages involved in the use of chlorite as anoxidizing agent, the most serious of which is that the solution tends toetch the surface of the metal, thus interfering with the formation of atenacious oxide layer which is suitable for adhesive joining. Thisetching action is more severe towards metals which are commonly alloyedwith copper such as zincand tin, to the extent that when such alloyingagents are present in the metal in total amounts greater than about 10percent, the use of such a solution is no longer practical. A furtherdisadvantage is that it is not economical to treat substantial amountsof metal surfaces due to the relatively high cost of this oxidizingagent.

SUMMARY OF THE INVENTION This invention is essentially a joiningtechnique in which the surface of copper and its alloys is treated withan alkaline permanganate solution prior to joining, and results injoints which are significantly improved over those obtained previously.In addition, this solution is more economical to use than previouslyused solutions.

Since the surface to be treated ordinarily contains contaminants such asdirt, grease and corrosion products, it is usually necessary to removethese prior to the permanganate treatment, and to aid the practictionerexemplary procedures are briefly described.

Furthermore, since the treatment is essentially one to prepare thesurface of copper and its alloys for joining to an organic adhesivematerial, bonds to dissimilar metals as well as to similar metals andalso bonds to nonmetals are contemplated.

DETAILED DESCRIPTION This process applies to copper and any of itsalloys containing at least 50 percent copper.

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Preliminary cleaning is by methods well known in the art. Thus, thefollowing description of preliminary cleaning is intended to beexemplary and not limiting.

Preliminary cleaning is generally divided into degreasing and descaling.For example, degreasing is generally effective in removing only oils andgrease and is ineffective in removing corrosion products such asnaturally formed oxide scale. Descaling, which may be either mechanicalor chemical, will, however, generally remove substantially all of thesurface contamination. However, descaling chemically without firstdegreasing may result in rapid contamination of the solution,replacement of which may be both costly and time consuming.

Removal of oils and grease may be accomplished by the use of organicsolvents such as alcohols, ketones and chlorinated solvents such astrichloroethylene and perchloroethylene. Such removal may also beaccomplished by use of alkaline cleaners. Commonly used components I ofsuch cleaning mixtures are: sodium hydroxide, used for its saponifyingpower; phosphates and silicates, used for their emulsifying and wettingabilities; surface active agents such as alkyl aryl polyether alcohols,used for their wetting ability; and detergents, used for their wettingand saponifying ability.

An example of an effective alkaline cleaning solution is one whichcontains from 1 to 10 percent by weight sodium metasilicate, from 1 to10 percent trisodium phosphate and from 1 to 10 percent of an alkyl arylpolyether alcohol, remainder water. Cleaning in this solution may becarried out for from 1 to 30 minutes at a temperature of from 70 to 180F.

Descaling is usually accomplished by the use of acid solutions or bymechanical abrasion. The particular method chosen for descaling willdepend on the thickness, composition and character of the scale, whichdepends upon the composition of the metal and upon its history,particularly its thermal history.

The usual practice is to use an aqueous solution containing from 1 to 10 percent by weight of nitric acid, immersing the metal therein at atemperature of from 70 F. to 150 F. for from 1 to 30 minutes. However,such a treatment is often ineffective in removal of the scale. It isthus preferred to add phosphoric acid to this solution, to increase theacidity of the solution. Such a solution contains from 1 to percent byweight phosphoric acid, from 1 to 40 percent by weight nitric acid,remainder at least 20 percent water, and is used within the sametemperature range as is the nitric acid solution.

Too high a concentration of nitric acid attacks the surface too rapidly,taking away substantial amounts of pure metal. Too high a concentrationof phosphoric acid or too low a concentration of nitric acid results inthe solution becoming less effective against severe contamination andrequires excessively long cleaning times for moderate surfacecontamination.

Phosphoric acid may also be used to contribute to the formation of asmooth and bright surface, if it is present in amounts above about 40percent by weight of the solution, within the ranges already specified.

Examples of mechanical abrasion methods for descaling are abrasiveblasting, wire brushing, and grinding. In general, these methods aremore wasteful of metal and produce surfaces somewhat rougher texturedthan do solution methods. However, rough surfaces are particularlyadvantageous for increased peel strength of subsequently formed joints.Sandblasting is often used for this reason. In operation, grit or sandwhich passes a standard screen from -No. 150 to 500 is introduced intoan air stream at pressures of 25 to about pounds per square inch and theblast directed over the surface of the metal until the scale is removed.

A rough surface may also be achieved chemically of course, as forexample, by adjusting the concentration of an acid pickling bath to ahigh concentration of nitric acid within the ranges described or byusing a chemical etching solution containing for example hydrochloricacid and either ferric chloride or cupric chloride each in the amountsof from 1 to 10 percent by weight.

A more complete description of degreasing and descaling methods may befound in Protective Coatings for Metals, Third Edition, AmericanChemical Society, Monograph 163 by R. M. Burns and W. W. Bradley, pp. 27to 54, Reinhold (1967).

Once the removal of surface contamination has been effected, the cleanmetal surface should be either treated with permanganate solutionpromptly or stored under noncorrosive conditions until treatment, sinceexposure of the clean surface to a nonprotective atmosphere will soonresult in reformation of corrosion products and exposure for longer thanabout two days will render the subsequent permanganate treatmentsubstantially ineffective.

The concentration of permanganate ions in the solution is not criticaland may range from0.001 percent by weight to saturation. The ions may beintroduced in combination with the Group I alkali metals; lithium,sodium, potassium, rubidium and cesium or the Group II alkaline earthmetals; beryllium, magnesium, calcium, strontium and barium. It isessential that the solution have a pH of at least 6 in order to insureagainst dissolution of the oxide layer which is formed.

Alkalinity may be achieved by using any compound which will yieldhydroxyl ions in solution as, for example, the Group I and Group IImetal phosphates, hydroxides and carbonates. Treatment may range from /2to 60 minutes at a solution temperature of from room temperature to itsboiling point, and results in an oxide layer of from about 150 to 1200angstroms in thickness, below which the layer is thin enough tosignificantly reduce joint strength and above which the layer ismechanically weak, resulting in weak joints. Optimum results however areachieved by a closer control of the parameters so that a layer of fromabout 400 to 500 angstroms in thickness results.

The rate of formation of the layer generally increases as theconcentration and temperature of the solution and the duration of thecontact increase. Layers having thicknesses substantially within thepreferred range may be obtained by treating the surface with a solutioncontaining permanganate ions in the amount of from 1 to 10 percent byweight and having a pH of at least 11, at a temperature of from 180 to200 F. for from 3 to minutes, the lower concentrations corresponding tothe higher solution temperatures and longer immersion times.

Example 1 TABLE 1 Sample No.

Potassium permanganate present in solution (wt. percent) 1 1 10 1 Sodiumhydroxide present in solution (wt percent) 1 1 10 10 1' Temperature ofsolution F.) 180 180 180 180 200 Time of immersion of sample (mins.) 510 3 6 5 Thickness 01 resulting layer (A.) 250 295 485 950 430 After thepermanganate treatment a rinsing step is preferred for optimum results.Air drying is satisfactory.

4 Inthis condition, the material is ready for subsequent joining.

Since the method described is essentially directed toward improvingadhesive joining by improving the surface of the metal, it is notlimited for use with certain adhesives, but is useful in preparingsurfaces for application of any organic materials such as the usualadhesives; epoxy and modified epoxy resins; nitrile rubber phenolics;polyvinyl butyrals; and polyvinyl formals.

Example 2 Three sets of six each samples of copper, .063 inch thick,were vapor degreased with trichloroethylene. The samples in Sets 1 and 2were then acid etched in a 20 percent by volume nitric acid solution for1 minute. Set 3 was acid etched in a solution containing nitric acid andphosphoric acid in the amounts of 75 percent and 10 percent by volume,respectively, for 1 minute. All of the samples were then rinsed withdistilled water. Set 1 was then treated in a solution containingchlorite ions for 3 minutes at 200 F. Sets 2 and 3 were treated in asolution containing 1 percent by Weight each of potassium permanganateand sodium hydroxide for five minutes at 180 P. All the samples in eachset were then rinsed with distilled water and air dried at roomtemperature. The samples were then joined with other identically treatedsamples by means of a modified epoxy resin using a standard one-halfinch lap joint and a bond thickness of 3 mils and measured for tensileshear strength according to ASTM Procedure D-10002. Rupture was alsomeasured by observing the time to failure when a static load of 3,000pounds per square inch was applied in an ambient atmosphere of 95 F. at90 percent relative humidity. Results are shown in Table 2.

TABLE 2 Set N0. 1 No. 2 No. 3

Average tensile shear (p.s.i.) 4, 840 5, 280 5, 360 Days to failure 4145 45 1 1 of the 6 joints failed after 23 days.

Example 3 Two sets of six each samples of Muntz metal (60 percentcopper, 40 percent zinc), .063 inch thick were vapor degreased withtrichloroethylene. They were then acidetched in the same manner as Set 3in Example 2, and then rinsed with distilled water. Set 1 was thentreated with a solution containing chlorite ions for two minutes at 200F. Set 2 was treated with a solution containing 1 percent by weight eachof potassium permanganate and sodium hydroxide for five minutes at P.All of the samples were then rinsed with distilled water, air dried atroom temperature, and tested as in Example 2, except that rupture wasmeasured for a static load of 800 p.s.i. Results are shown in Table 3.

These results show that improvement is obtained in tensile shear valuewhich is comparable to that obtained for the copper samples of Example2. They also indicate, however, a significantly greater improvement indays to failure under a static load than was obtained for copper,

and accordingly illustrate the advantage of the substantiallynoncorrosive nature of a permanganate solution towards the zinc alloyingagent.

Example 4 Three sets of six each samples of beryllium copper (1.9percent beryllium) .063 inch thick were vapor degreased withtrichloroethylene. They were then acid-etched as was Set 3 in Example 2,and rinsed with distilled Water. Set 1 was then treated in a solutioncontaining chlorite ions for three minutes at 200 F. Set 2 was treatedin a solution containing 1 percent by weight each of potassiumpermanganate and sodium hydroxide for five minutes at 180 F. Set 3 wastreated in the same permanganate solution for five minutes at about 200P. All of the samples were then rinsed with distilled water and airdried at room temperature. They were then tested as in the previousexamples for an average tensile shear value. The results are shown inTable 4.

TABLE 4 Average tensile shear (p.s.i.) Set No. l 5700 Set No. 2 5880 SetNo. 3 6140 The permanganate treatments for Sets 2 and 3 correspond totreatments for Sets 1 and 5, respectively, in Example 1. It is thereforeapparent that the permanganate treatment resulting in an oxide layerhaving a thickness of about 400 angstroms gives results which aresignificantly improved over those obtained for a sample having a layerwhose thickness is less.

Example 5 The results are shown in Table 5.

TABLE 5 Set No. 1 No.2

Average tensile shear (p.s.i.) 3, 580 5, 570 Days to failure (under astatic load of 3,500 p.s.i.) 60 Days to failure (under a static load of4,000 p.s.i.) 42

1 Less than 1 hour.

The results indicate that permanent joints under static loading areobtainable by use of the permanganate treat- 6 ment for alloyscontaining substantial amounts of alloying agents.

The invention has been described with reference to particularembodiments thereof, but it is intended that variations therefrom whichbasically rely on the teachings of the invention are to be considered aswithin the scope of the invention and the appended claims.

What is claimed is:

1. A method for joining a surface containing at least 50 percent byweight copper to an organic material, characterized in that said joiningis preceded by the step of contacting said surface with an aqueoussolution containing permanganate ions and positive ions, said positiveions consisting essentially of one or more ions selected from the groupconsisting of sodium and potassium ions, said solution having a pH of atleast 6.

2. The method of claim 1 in which said solution contains permanganateions in the amount of from 0.001 percent by weight to saturation.

3. The method of claim 2 in which said solution contains permanganateions in the amount of from 1 to 10 percent by weight.

4. The method of claim 1 in which the step of contacting said surfacewith said solution is carried out at a temperature of from 25 F. to theboiling point of said solution for from one-half to sixty minutes, thelower temperatures corresponding to longer immersion times.

5. The method of claim 4 in which said step of contacting said surfacewith said solution is carried out at a temperature of from F. to 200 F.for from three to five minutes, the lower temperatures corresponding tolonger immersion times.

6. The method of claim 1 in which the pH of said solution is at least11.

7. The method of claim 1 in which the pH of said solution is achieved byuse of a compound of a member selected from the group consisting ofphosphates, hydroxides and carbonates.

8. The method of claim 1 in which the step of contacting said surfacewith said solution is preceded by descaling.

9. Product produced by the method of claim 1.

References Cited UNITED STATES PATENTS 1,319,508 10/1919 Bengough et al.148-6.14 2,127,206 8/1938 Curtin 148-614 2,784,156 3/1957 Maurin(148--6.14) 3,198,672 8/1965 De Hart 148-6.l4 3,284,249 11/1966 Osborn148-614 X RALPH S. KENDALL, Primary Examiner

